Catalyst and method for preparing same



catalysts in the forn'i Patented Mar. 17, 1936 UNITE 2,034,077 CATALYSTAND METHOD FOR PREPARING SAME Herrick a. Arnold, Elmlmrst and wubma.Lazier, Mton. DeL, 'asaignors to E. I. du Pont de Nemours & Comi y,Wilmington, Del., a corporation of Delaware No Drawing. ApplicationJanuary 2'], 1932,

Serial No. 589,300"

16 Claims. (on. 23-236)- This invention relates to catalysts andcatalytic processes and more particularly to improvements inthepreparation and use of hydrogenation catalysts of the non-ferrousmetal type.

Catalytic agents adapted for use in hydrogenation reactions may bedivided into three main groups. The first and most important group froman industrial standpoint comprises the ferrous metals, and includesfinely divided metallic iron, cobalt and nickel catalysts. Secondly,there are the noble metals such as platinum, palladium, osmium, etcwhich are sometimes favored as catalysts for hydrogenations conducted ona laboratoryscale. Owing to their great cost, these metals have foundonly limited application in the arts.

The third group, with which the present invention is concerned,comprises the non-noble, non ferrous metal catalysts. Typical members ofthis class are copper, 'zinc, manganese, cadmium, tin, lead and silver.These elements may serve as of oxides or in a partially or whollyreduced condition. Metallic copper, for example, has been extensivelyemployed in hydrogenation and dehydrogenation reactions. The use of zincoxide as a catalyst for methanol synthesis and other high-pressure gasphase reactions of course is well known. Certain other nonferroushydrogenating metals have been mentioned as catalysts for specifichydrogenation reactions.

The non-ferrous metals are much milder in their action than those of theferrous metal group and for this reason are employed in order to obtainspecific effects depending on the selectivity of the catalyst. On theother hand, they are somewhat less active and offer certain othertechnical difliculties in connection with their use. Zinc and manganeseoxides are quite ineffective as hydrogenation catalysts in liquid media,and the corresponding metals are very dlfiicult to prepare in a finelydivided condition, owing to the difllculty with which they may bereduced with hydrogen. Metals of the non-ferrous group have relativelylow melting points and are therefore susceptible to loss of activitythrough sintering by heat.

The present invention has as its object to overcombinations of metalsand oxides,and by the use of precipitation methods that promote anintimacy of contact and uniformity of texture unobtainable by othermeans. Another object pertains to the new catalyst compositionsdescribed 5 herein. Other objects will become apparent from the detaileddescription of invention given below.

These objects are accomplished in the following manner. It has beenfound particularly advantageous in the preparation of non-ferrous metalcatalysts to employ as starting materials salts of metals that arecapable of forming soluble complex ions with nitrogen bases such asammonium hydroxide. Copper nitrate and zinc nitrate are examples of suchsalts. When ammonium hydroxide is-added in excess to a solution of oneor more of these salts, a clear solution is obtained. On heating thissolution and slowly discharging the ammonia a precipitate of a sandycharacter is formed consisting of the metal hydroxide. The formation ofthe precipitate is further facilitated and its catalytic usefulnessimproved by suspend ing a finely divided inert supporting material'inthe clear solution prior to discharging the ammonia. The particles ofsupporting material present 5 in the mother liquor at the time ofprecipitation serve as nuclei around which the precipitated hydroxidemay form.

Although the invention is susceptible of wide variation in the manner ofits application to the preparation and use of hydrogenation catalysts,bothwith respect to specific combination of materials and conditionsused, the following examples will serve to illustrate how the inventionmay be carried out in practice.

Example 1 A solution of copper nitrate is prepared by dissolving 480grams of the crystallized salt in about 6 liters of water. Twelvehundred sixty cc. of 28% ammonium hydroxide is added with stirring. Thecopper hydroxide at first precipitated, redissolves to give a deep blueclear solution. To this there is.added60 grams of dry powderedkieselguhr. The mixture is heated to about 70 C. and is maintained atthis temperature while an energetic stream of air is forced through thesuspension. After several hours it is found that the greater part of theammonia has been expelled andas a consequence hydrated copper oxide .isfound to have been deposited in the form of a dense granular precipitateon the suspended heselguhr. The precipitate is washed several times bydecantation, and is filtered,dried, and reduced with diluted hydrogenfor four hours at a temsence of the copper.

perature of 200-300 C. A sample of reduced catalyst prepared asdescribed analyzed 66.5% metallic copper.

Example 2 A mixed salt solutionis prepared by dissolving 24., grams ofcopper nitrate and 297 grams of zinc nitrate in about 6 liters ofdistilled water.

- Fifteen hundred cc. of 28% ammonia is added which, on account of beingin excess of the salts, gives a clear solution; Sixty grams ofkieselguhr is added at this point and the mixture is heated at C. andblown with air as described in Example 1 until all of the excess ammoniahas been removed. The precipitate comprising an intimate, sandy mixtureof zinc hydroxide, copper hydroxide, and kieselguhr is washed, filtered,dried and reduced in hydrogen for 18 hours at 200-300 C. Analysis of thereduced catalyst revealed a copper content of 19.5% and a zinc contentof 36.9%. By means of a special method of analysis it was found that thereduced zinc content was 0.85%, a value that could be obtained only byreduction of zinc oxide in. intimate contact with an easily reducibleoxide such as copper oxide.

, On subjecting the mixed supported hydrated copper oxide-zinc oxideprecipitate to reduction with hydrogen, it has been found that the zincoxide reduces to a,far greater extent than is possible under the sameconditions in the ab- The reduced product is grey in color rather thanthe characteristic reddish-brown of active metallic copper and possessesan activity far greater than that of the usual reduced copper catalyst.

Example 3 Two hundred and twenty-two grams of zinc nitrate, 25 grams ofcopper nitrate and 48 grams of cadmium nitrate are dissolved in 4 litersof water. To this solution there is added with stirring 800 cc. of 28%ammonium hydroxide and 100 grams of finely powdered activated charcoal.The suspension is heated to C. and treated with air at this temperatureuntil the solution is practically neutral. The hydroxides of copper,zinc and cadmium admixed 'with and precipitated upon the activatedcharcoal are filtered, washed and dried. The catalyst thus prepared maybe briquetted for use in a vapor phase process or it maybe reduced withhydrogen in the powder phase hydrogenation reaction.

Example 4 A solution is prepared by dissolving 183 grams oi anhydrouscadmium chloride and 150 grams of anhydrous stannous chloride in 8liters of water. One thousand cc. of ammonium hydroxide is added to thissolution, which causes the precipitation of both cadmium and stannoushydroxide. The cadmium hydroxide, however, redissolves in the excessammonia, leaving the stannous hydroxide suspended in the solution. Themixture is heated to 50 C. or over and the excess ammonia is dischargedas described in the preceding examples. By this treatment cadmiumhydroxide is reprecipitated in a granular form, the particles ofstannous hydroxide serving as nuclei for the formation of the minutecrystals. In order to obtain a tin-cadmium catalyst, the mixedhydroxides so prepared are subjected to careful reduction with hydrogenat a temperature insufiicient to cause substantial sintering of thefinely divided metals and for a period suitable for converting a portionof the hydroxides to metals.

Example 5 Eight hundred cc. of strong ammonium hydroxide is added to 10liters of a 2% solution of silver nitrate. There is added to thesolution at this point 200 grams of powdered aluminum oxide gel. Thesolution is brought to the boiling point and is boiled until the greaterpart of the ammonia has been expelled, which process results in thesubstantial precipitation of the silver as silver oxide. The alumina isinsoluble in the ammonium hydroxide solution and serves as a cata lystsupport upon which the finely divided silver oxide is precipitated.

Example 6 A copper-zinc-zinc oxide kieselguhr catalyst prepared asdescribed in Example 2 was employed for the hydrogenation of furfural tofurfuryl alcohol. Two hundred grams of vacuum distilled furfural, cc. ofwater and 20 grams of the catalyst were charged into a small autoclaveand subjected to a hydrogen pressure of 1800 lbs. per square inch. Themixture was agitated violently for 2 hours at a temperature of 150 C.Hydrogen absorption was complete after two or three hours. The catalystwas removed by filtration after which the liquid products were recoveredby fractional distillation. Five per cent of the original furfural wasrecovered unchanged and 70 per cent was found to have been converted tofurfuryl alcohol. A copper-kieselguhr catalyst prepared as described inExample 1 gave similar results in the hydrogenation of furfural.

Example 7 One hundred grams of dextrose was dissolved in 200 cc. ofwater. Twenty grams of a copperzino-kieselguhr catalyst prepared asdescribed in Example 2 was added and the mixture agitated with hydrogenat a pressure of 1400 lbs. and a temperature of -150 C. Sorbitolcontaining negligible amounts of dextrose was obtained by filtration andevaporation of the reduced solution.

The invention is applicable to any precipitated catalyst comprising anoxide or hydroxide of a metal that is soluble in excess of ammoniumhydroxide and that can be regenerated as the hydroxide by decreasing theammonia concentration. Such elements are, for example, zinc, copper,silver, and cadmium. They may, however, be used in combination withother nonferrous hydrogenating metal hydroxides which do not possess theproperty of dissolving in an excess of the precipitating agent.

In carrying the invention out in practice, the soluble salts of one ormore metals forming a complex ion with ammonia may be dissolved inwater, an excess of ammonia added, and inert suspended matter added tothe clear solution prior to discharging the excess ammonia.Alternatively, the precipitated hydroxide of a nonferrous metal notbelonging to the class of complex ion formers may be used in conjunctionwith one of the metals named above, the insoluble hydroxide then formingthe nuclei about which the new precipitate is formed during eliminationof the excess of reagent.

The catalytic metal hydroxides may be precipitated upon suitablesupports either singly or in combination of two or more. the mostsatistures of readily reducible hydroxi together with more dimcultlyreducible oxides. In this way the reduction of the dimcultly reducibleoxide is greatly facilitated, end the procedure results in catalystsheving the properties of active metals not otherwise obteineble. Forexample,

by coprecipitating copper and fine hydroxides from an excess of ammoniaand reducing the re sulting mixture, 2. reduced catalyst is obtainedhaving the properties of a. metallic zinc catalyst, even though theextent of reduction of the zinc oxide is quite small.

Composite hydroxide cetalysts prepared by the present invention may begranulated or bri quettecl for use in vapor phase hydrogenation or theymay m reduced in the powder form for use in liquid medic. In carryingout our hydrcgenutions the usual procedure will be to agitate the liquidor solutionto be hydrogenated with a small portion oi the reduced powderin a compressed atmosphere of hydrogen.

The exact concentrations of reagents to be used are subject to widevariations depending upon the particular elements comprising thecatelyst composition to be made. in general, the more dilute the initialsalt solution, the larger the excess of ammonia, that will be requredfor formation of the soluble complex.

Instead of using 'eir, other gases such as carbon dioxide hydrogen, ornitrogen may he used for expelling the excess of the volatile loose. insome instances this may be performed merely by boiling the solution.Other volatile, water=soluhle bases chemicelly similar to ammonia, forexemple a solution of methyl amine, may he used for forznewion. of thecolt-color: soluble salt.

As catalyst carriers, e. number of materials such as meselguhr, powderedsilice. gel, alum na gel, activated charcoal, or iullers earth may beused. The functions or the supporting meter-lei are two-fold. The fineparticles suspended in the mother liquor dining reoipitetion form nucleiabout which the formation of crystals of the we cipiteted hydroxidetolse piece. Secondly, during subsequent reduction with hydrogen, theinert supporting material prevents the coolescence of the tin perticlesof reduced metal, there-= oy helping to maintain the surface in e ruggedstate.

The catalysts oi the present invention are ap plicable to a wide varietyof uses. They are particularly'useful for reactions of hydrogenation anddehydrogenation. Such compounds as those containing the carbonyl groupare particularly susceptible to hydrogenation by non-ferrous metalcatalysts. Aldehydes and ketones may be reduced to the correspondingalcohols, sugars to polyalcohols, acids and esters to the correspondingalcohols or hydrocarbons. Various compounds containng other unsaturatedgroups such as the nitrocompounds and nltriles may alsobe hydrogenated.The non-ferrous metal hydrogenation catalysts of the present inventionfind specialized applications in hvdrogenat'ons of a. selective nature.For example, aromatic aldehydes and ketones may be hydrogenated toaromatic alcohols, and furfural may be converted to furfuryl alcohol ormethyl furfurane. In these and other instances the carbonyl group isreduced without saturation of the unsaturated r'ng. A large number ofdehydrogenation reactions may becarrled out by use of the catalysts ofthis invention among which may be mentioned the conversion of alcoholsto aldehydes or ketones,

ors

the synthesis 01 phor from isobomeol, and the conversion of hydrourticcompo to the corresponding aromatic compounds.

The usual methods of precipitation of metallic hydroxides yieldgelatinous precipitates that can be eflectively washed only with thegreatest dim culty. In the present instance the precipitates areproduced in a finely granular condition and hove a relatively highdensity, which greatly facilitates washing and filtration. The use offixed olkolles is likewise avoided. Gonsequently products of high purityare obtained which are free from catalyst poisons-or other noxiousimpurities.

The above description end examples are to be taken as illustrative onlyend not as limiting the scope of the invention. Any modification orvariation therefrom which conforms to the spirit of the invention isintended to be included within the scope of the claims.

We claim: g

l. A catalyst composition suitable for hydrosanction and dehydrogenationreactions prepared by suspending an inert supportng material in anammonlacal solution of a. copper salt and a zinc salt, said solutioncontsining ammonia in excess of that stoichlometricelly requ'red toprecipitete the hydroxides, coprecipiteting on the supporting materialhydroxides of copper and zinc, and sepernt'ng the mixture of copper andzinc hydroxides and supporting materiel from the solution.

2. A process for preparing a. catalyst composition sultnble forhydrogenation and dehydrogenotion reactions, which comprlses'suspendingan inert supporting material in on srnmonlcoal solution of s. coppersalt and e. zinc sslt, said solution contain ng ammonia in excess ofthat stoichionietricnlly required to precipitate the hydroxides, thencoprecipitnting on the supporting material hydroxides of copper and zincby removing ammonia. from the solution, and sepesolution an inertsupporting material, then coprecipitating on the supporting materialhydroxides of-copper and zinc, separating the mixture of supportingmaterial and hydroxides of copper and zinc from the solution, andsubject ing the precipitate to reduction wth hydrogen.

4. A catalyst composition suitable for hydro-' genatlon anddehydrogenation reactions prepared by dissolving a copper salt and azinc. salt in water, adding ammonia to the solution in an amount inexcess of that required to redlssolve the hydroxides, suspending aninert supporting material in sold solution, then removing the excessammonia. untiLa precipitate forms, and separating the precipitate andinert supporting material from the solution.

5. The catalyst of claim 4 characterized in that the precipitate hasbeen subjected to reduction with hydrogen after separation from thesolu-' tion.

6. A process for preparing a. catalyst composition suitable forhydrogenation and dehydrogenation reactions, which comprises dissolvinga copper salt and a zinc salt in water, adding ammonia.

to the solution in an amount in excess of that required to redissolvethe precipitated hydroxides, suspending in said solution an inertsupporting material, removing the excess aminonia'from the solution, andseparatin the thus hydroxides from the solution.

7. A catalyst composition suitable for hydrogenation and dehydrogenationreactions prepared by dissolving, in water, salts oi at least twononferrous metals whose hydroxides are soluble in excess ammonia, addingammonia to the solution in an amount in exce s of that required toredissolve the precipitated metal hydroxides, suspending an inertsupporting material in such solution, removing the excess ammonia untila precipitate forms, and separating the precipitate and supportingmaterial from the solution.

8. A catalyst composition suitable for hydrogenation and dehydrogenationreactions prepared by dissolving, in water, salts of at least twononierrous metals whose hydroxides are soluble in excess ammonia, addingammonia to the solution in an amount in excess of that required toredissolve the precipitated metal hydroxides, suspending an inertsupporting material in such solution, removing the excess ammonia untila precipitate forms, separating the precipitate and the inert supportingmaterial from the solution, and subjecting the precipitate to reductionwith hydrogen.

9. A catalyst composition suitable for hydrogenation and dehydrogenationreactions prepared by dissolving, in water, salts of at least twononferrous metals whose hydroxides are soluble in excess ammonia, addingammonia to the solution in an amount in excess oi that required toredissolve the precipitated metal hydroxides, suspending an inertsupporting material in such solution, and then removing theexcessammonia. by passing a current of inert gas thru the solution untila precipitate forms, separating the precipitate and the inert supportingmaterial from the solution, and subjecting the precipitate to reductionwith hydrogen.

' 10. A catalyst composition suitable for hydrogenation anddehydrogenation reactions prepared by dissolving, in water, salts of atleast two nonferrous metals whose hydroxides are soluble in excessammonia, adding ammonia to the solution in an amount in excess of thatrequired to redissolve the precipitated metal hydroxides, suspending aninert supporting material in such solution, and then removing the excessammonia by passing a current of air thru the solution until aprecipitate forms, separating the precipitate and the inert supportingmaterial from the solution,

and subjecting the precipitate to reduction with hydrogen.

11. A process for preparing a catalyst composition suitable forhydrogenation and dehydrogenation reactions, which comprises dissolving,in water, salts of at least two non-ferrous metals whose hydroxides aresoluble in excess ammonia, adding ammonia to the solution in an amountin precipitated excess oi that required to redissolve the precipitatedmetal hydroxides, suspending an inert supporting material in suchsolution, then re- ,moving the excess ammonia from the solution,

and separating the precipitate and the inert supporting material fromthe solution.

12. A process for preparing a catalyst composition suitable forhydrogenation and dehydrogenation reactions, which comprises dissolving,in

, water, salts of at least two non-ferrous metals whose hydroxides aresoluble in excess ammonia,

adding ammonia to the solution in an amount in excess of that requiredto redissolve the precipitated metal hydroxides, suspending an inertsupporting material in such solution, removing the excess ammonia fromthe solution, separating the precipitate and inert supporting materialfrom the solution, and subjecting .the precipitate to reduction withhydrogen.

13. A process ior preparing a catalyst composition suitable forhydrogenation and dehydrogenation reactions, which comprises dissolving,in

water, salts of at least two non-ferrous metals whose hydroxides aresoluble in excess ammonia, adding ammonia to the solution in an amountin excess of that required to redissolve the precipitated metalhydroxides, suspending in said solution an inert supporting material,then removing the excess ammonia from the solution by passing a currentof inert gas thru the solution, filtering the precipitate and inertsupporting material from the solution, and subjecting the precipitate toreduction with hydrogen.

14. A process for preparing a catalyst composition suitable forhydrogenation and dehydrogention suitable for hydrogenation anddehydrogenation reactions, which comprises suspending an inertsupporting material in a solution containing the salts of at least twometals whose hy droxides are soluble in excess ammonia, adding ammoniato said solution in amount sufilcient to redissolve the precipitatedhydroxides, precipitating the hydroxides by removal of ammonia, andseparating the precipitate and inert supporting material from thesolution.

16. The process .of claim 15 wherein the precipitated material isreduced with hydrogen after separation from the solution.

HERRICK R. ARNOLD. WILBUR A. LAZIER.

